Hotbar: tools, models and materials on your hotbar (at the bottom of the screen) can be replaced with different ones. This is done by opening your inventory and dragging a tool, model or material onto your hotbar.

Tools and models are listed in the left half of the inventory and can only be placed in the first 5 cells of your hotbar.

Materials are listed in the right half of the inventory and can only be placed in the last 5 cells of your hotbar.

There is currently no way to rebind the controls or change the mouse sensitivity.